Tumefactive demyelination is an aggressive, localized, generally solitary area of demyelination that often mimics a neoplasm. We present a case of a 13-year-old female patient who presented with sudden-onset progressive hemiplegia and hemianopsia. Magnetic resonance imaging of the brain showed tumefactive demyelination with partial rim of enhancement. During inpatient rehabilitation, she developed myalgias, rash, and abdominal and mouth pain with evidence for severe neutropenia. The neutropenia was determined to be a secondary complication of the tumefactive disease process. This scenario may be concerning in an inpatient rehabilitation setting, as patients share common areas, increasing the risk of acquired infection while neutropenic. LEVEL OF EVIDENCE: V. CI - Copyright (c) 2018 American Academy of Physical Medicine and Rehabilitation. Published by Elsevier Inc. All rights reserved.